1. Field of the Invention
The present invention is directed generally to solar cells and more specifically to a method for manufacturing a solar cell from a substrate wafer.
2. Description of the Related Art
Among other things, substrate wafers of monocrystalline silicon are used for manufacturing solar cells. The monocrystalline solar cells manufactured therefrom are superior with respect to efficiency and long-term stability to others manufactured using polycrystalline or amorphus silicon.
An electrical contact is usually situated on each side in monocrystalline solar cells. The light is thereby incident through a surface at which a contact is arranged (see, for example, R. Mueller, Bauelemente der Halbleiterelektronik, Springer Verlag 1979, pages 45-47).
Since a contact is arranged on the surface of the solar cell facing toward the light, a part of this surface is occluded. This results in a lower overall efficiency of the solar cell.
In order to keep this occlusion slight, the contact on the surface facing toward the light is structured, for example, in a comb-like manner. The line cross section of the contact is thereby kept at a minimum. Increased ohmic losses, however, are connected therewith, these in turn lead to a deterioration of the efficiency.
Since the electrical contacts are arranged at opposite sides, a plurality of solar cells of this type can only be interconnected by using a conductive connecting element, for example, a wire. To that end, a certain spacing between neighboring solar cells must be observed so that the connecting element can be conducted onto the backside of the neighboring cell. The available area to be occupied with solar cells cannot be as dense as desired.
T. Fukui et al, Techn. Dig. of Fourth Sunshine Workshop on Crystalline Solar Cells (1992), Chiba, Japan, pp. 25-29 disclose a solar cell that has through-holes from the front side to the back side of the solar cell having a spacing of 150 .mu.m. The solar cell is manufactured of p-doped silicon. The solar cell has an n-doped region at the front side of the solar cell and along the surface of the holes. Proceeding from the back side, the n-doped region is connected by n-contacts and the p-doped region is connected by p-contacts. Such through-holes through silicon substrates can be produced, in particular, by using a laser. Each hole must thereby be separately generated.